Update using-handlebars.md
Update using-handlebars.md

Call out the reason for the "triple-stash" in HTML substitution
sendgrid/docs,sendgrid/docs,ksigler7/docs,Whatthefoxsays/docs,sendgrid/docs,ksigler7/docs,ksigler7/docs,Whatthefoxsays/docs,Whatthefoxsays/docs